Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/l…

…inux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:

 - LKMM updates: mostly documentation changes, but also some new litmus
   tests for atomic ops.

 - KCSAN updates: the most important change is that GCC 11 now has all
   fixes in place to support KCSAN, so GCC support can be enabled again.
   Also more annotations.

 - futex updates: minor cleanups and simplifications

 - seqlock updates: merge preparatory changes/cleanups for the
   'associated locks' facilities.

 - lockdep updates:
    - simplify IRQ trace event handling
    - add various new debug checks
    - simplify header dependencies, split out <linux/lockdep_types.h>,
      decouple lockdep from other low level headers some more
    - fix NMI handling

 - misc cleanups and smaller fixes

* tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
  kcsan: Improve IRQ state trace reporting
  lockdep: Refactor IRQ trace events fields into struct
  seqlock: lockdep assert non-preemptibility on seqcount_t write
  lockdep: Add preemption enabled/disabled assertion APIs
  seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
  seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs
  seqlock: Reorder seqcount_t and seqlock_t API definitions
  seqlock: seqcount_t latch: End read sections with read_seqcount_retry()
  seqlock: Properly format kernel-doc code samples
  Documentation: locking: Describe seqlock design and usage
  locking/qspinlock: Do not include atomic.h from qspinlock_types.h
  locking/atomic: Move ATOMIC_INIT into linux/types.h
  lockdep: Move list.h inclusion into lockdep.h
  locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs
  futex: Remove unused or redundant includes
  futex: Consistently use fshared as boolean
  futex: Remove needless goto's
  futex: Remove put_futex_key()
  rwsem: fix commas in initialisation
  docs: locking: Replace HTTP links with HTTPS ones
  ...

Documentation/atomic_t.txt

@@ -85,21 +85,21 @@ smp_store_release() respectively. Therefore, if you find yourself only using
 the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
 and are doing it wrong.
 
-A subtle detail of atomic_set{}() is that it should be observable to the RMW
-ops. That is:
+A note for the implementation of atomic_set{}() is that it must not break the
+atomicity of the RMW ops. That is:
 
-  C atomic-set
+  C Atomic-RMW-ops-are-atomic-WRT-atomic_set
 
   {
-    atomic_set(v, 1);
+    atomic_t v = ATOMIC_INIT(1);
   }
 
-  P1(atomic_t *v)
+  P0(atomic_t *v)
   {
-    atomic_add_unless(v, 1, 0);
+    (void)atomic_add_unless(v, 1, 0);
   }
 
-  P2(atomic_t *v)
+  P1(atomic_t *v)
   {
     atomic_set(v, 0);
   }
@@ -233,34 +233,34 @@ as well. Similarly, something like:
 is an ACQUIRE pattern (though very much not typical), but again the barrier is
 strictly stronger than ACQUIRE. As illustrated:
 
-  C strong-acquire
+  C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
 
   {
   }
 
-  P1(int *x, atomic_t *y)
+  P0(int *x, atomic_t *y)
   {
     r0 = READ_ONCE(*x);
     smp_rmb();
     r1 = atomic_read(y);
   }
 
-  P2(int *x, atomic_t *y)
+  P1(int *x, atomic_t *y)
   {
     atomic_inc(y);
     smp_mb__after_atomic();
     WRITE_ONCE(*x, 1);
   }
 
   exists
-  (r0=1 /\ r1=0)
+  (0:r0=1 /\ 0:r1=0)
 
 This should not happen; but a hypothetical atomic_inc_acquire() --
 (void)atomic_fetch_inc_acquire() for instance -- would allow the outcome,
 because it would not order the W part of the RMW against the following
 WRITE_ONCE.  Thus:
 
-  P1			P2
+  P0			P1
 
 			t = LL.acq *y (0)
 			t++;

Documentation/dev-tools/kcsan.rst

@@ -8,7 +8,8 @@ approach to detect races. KCSAN's primary purpose is to detect `data races`_.
 Usage
 -----
 
-KCSAN requires Clang version 11 or later.
+KCSAN is supported by both GCC and Clang. With GCC we require version 11 or
+later, and with Clang also require version 11 or later.
 
 To enable KCSAN configure the kernel with::
 

Documentation/litmus-tests/README

@@ -0,0 +1,35 @@
+============
+LITMUS TESTS
+============
+
+Each subdirectory contains litmus tests that are typical to describe the
+semantics of respective kernel APIs.
+For more information about how to "run" a litmus test or how to generate
+a kernel test module based on a litmus test, please see
+tools/memory-model/README.
+
+
+atomic (/atomic derectory)
+--------------------------
+
+Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
+    Test that an atomic RMW followed by a smp_mb__after_atomic() is
+    stronger than a normal acquire: both the read and write parts of
+    the RMW are ordered before the subsequential memory accesses.
+
+Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
+    Test that atomic_set() cannot break the atomicity of atomic RMWs.
+    NOTE: Require herd7 7.56 or later which supports "(void)expr".
+
+
+RCU (/rcu directory)
+--------------------
+
+MP+onceassign+derefonce.litmus (under tools/memory-model/litmus-tests/)
+    Demonstrates the use of rcu_assign_pointer() and rcu_dereference() to
+    ensure that an RCU reader will not see pre-initialization garbage.
+
+RCU+sync+read.litmus
+RCU+sync+free.litmus
+    Both the above litmus tests demonstrate the RCU grace period guarantee
+    that an RCU read-side critical section can never span a grace period.

Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus

@@ -0,0 +1,32 @@
+C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+
+(*
+ * Result: Never
+ *
+ * Test that an atomic RMW followed by a smp_mb__after_atomic() is
+ * stronger than a normal acquire: both the read and write parts of
+ * the RMW are ordered before the subsequential memory accesses.
+ *)
+
+{
+}
+
+P0(int *x, atomic_t *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	smp_rmb();
+	r1 = atomic_read(y);
+}
+
+P1(int *x, atomic_t *y)
+{
+	atomic_inc(y);
+	smp_mb__after_atomic();
+	WRITE_ONCE(*x, 1);
+}
+
+exists
+(0:r0=1 /\ 0:r1=0)

Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus

@@ -0,0 +1,25 @@
+C Atomic-RMW-ops-are-atomic-WRT-atomic_set
+
+(*
+ * Result: Never
+ *
+ * Test that atomic_set() cannot break the atomicity of atomic RMWs.
+ * NOTE: This requires herd7 7.56 or later which supports "(void)expr".
+ *)
+
+{
+	atomic_t v = ATOMIC_INIT(1);
+}
+
+P0(atomic_t *v)
+{
+	(void)atomic_add_unless(v, 1, 0);
+}
+
+P1(atomic_t *v)
+{
+	atomic_set(v, 0);
+}
+
+exists
+(v=2)

Documentation/litmus-tests/rcu/RCU+sync+free.litmus

@@ -0,0 +1,42 @@
+C RCU+sync+free
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that an RCU reader can never see a write that
+ * follows a grace period, if it did not see writes that precede that grace
+ * period.
+ *
+ * This is a typical pattern of RCU usage, where the write before the grace
+ * period assigns a pointer, and the writes following the grace period destroy
+ * the object that the pointer used to point to.
+ *
+ * This is one implication of the RCU grace-period guarantee, which says (among
+ * other things) that an RCU read-side critical section cannot span a grace period.
+ *)
+
+{
+int x = 1;
+int *y = &x;
+int z = 1;
+}
+
+P0(int *x, int *z, int **y)
+{
+	int *r0;
+	int r1;
+
+	rcu_read_lock();
+	r0 = rcu_dereference(*y);
+	r1 = READ_ONCE(*r0);
+	rcu_read_unlock();
+}
+
+P1(int *x, int *z, int **y)
+{
+	rcu_assign_pointer(*y, z);
+	synchronize_rcu();
+	WRITE_ONCE(*x, 0);
+}
+
+exists (0:r0=x /\ 0:r1=0)

Documentation/litmus-tests/rcu/RCU+sync+read.litmus

@@ -0,0 +1,37 @@
+C RCU+sync+read
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that after a grace period, an RCU updater always
+ * sees all stores done in prior RCU read-side critical sections. Such
+ * read-side critical sections would have ended before the grace period ended.
+ *
+ * This is one implication of the RCU grace-period guarantee, which says (among
+ * other things) that an RCU read-side critical section cannot span a grace period.
+ *)
+
+{
+int x = 0;
+int y = 0;
+}
+
+P0(int *x, int *y)
+{
+	rcu_read_lock();
+	WRITE_ONCE(*x, 1);
+	WRITE_ONCE(*y, 1);
+	rcu_read_unlock();
+}
+
+P1(int *x, int *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	synchronize_rcu();
+	r1 = READ_ONCE(*y);
+}
+
+exists (1:r0=1 /\ 1:r1=0)

Documentation/locking/index.rst

@@ -14,6 +14,7 @@ locking
     mutex-design
     rt-mutex-design
     rt-mutex
+    seqlock
     spinlocks
     ww-mutex-design
     preempt-locking

Documentation/locking/mutex-design.rst

@@ -18,7 +18,7 @@ as an alternative to these. This new data structure provided a number
 of advantages, including simpler interfaces, and at that time smaller
 code (see Disadvantages).
 
-[1] http://lwn.net/Articles/164802/
+[1] https://lwn.net/Articles/164802/
 
 Implementation
 --------------